It is well known that tip clearance leakage is one of the primary loss mechanisms in axial flow compressors and turbines of a gas turbine engine. Tip clearance loss translates into lost efficiency, higher fuel costs and thus higher operating costs. More particularly, over the operating life of an engine such as an aircraft engine, tip clearance increases over time, due at least in part to mechanical rubs between rotating blades and stationary casing and erosion. This clearance deterioration is a leading driver for engine performance deterioration, which often manifests in increased fuel burn and exhaust gas temperatures (EGT). The FAA mandates that an engine be removed for maintenance/overhaul once the EGT reaches an upper limit.
It is desirable therefore to maintain tip clearance as low as possible in an effort to minimize related losses throughout the engine-operating envelope. One way of achieving this is to use Active tip Clearance Control (ACC) systems, such that clearance levels are adjusted for engine operating conditions, and throughout the operating cycle. For any ACC concept to work effectively, real-time tip clearance data is required as part of the control algorithm. However, current tip clearance sensors are believed to be deficient in certain regards.
Accordingly, an alternative tip clearance measurement technique and system for accomplishing tip clearance measurement is highly desirable.